Month: January 2013

Like a magician our mind tricks us into believing what we see and feel. We only notice that something strange is going on when our expectations are betrayed during the prestige – when the white rabbit is drawn out of the empty hat. Psychology sometimes works in much the same way. After the mind has made us believe in the ordinary, it creates strange cases which point to something bigger going on behind the scenes. One of the most extraordinary illusions is the one of our body. At the final prestige we see people born with phantom penises which no one can see. What was going on behind the scenes?

‘Phantoms’ is what Silas Weir Mitchell called the amputated limbs that their owners could still feel. The most straight-forward explanation simply refers to re-membering. When an amputated limb lives on as a phantom arm one could say that the mind fails to realise the loss and fills in the usual feelings with memories. This re-membering may well explain why some people claim to feel a watch or even clothes on the phantom skin.

It is as if the magician had produced a rabbit out of an ‘empty’ hat and everyone suddenly noticed that the hat was high enough to house it from the start. However, the mind had another trick up its sleeve. Since the initial description of phantom limbs in 19th century amputees, this phenomenon has also been discovered in people who had never been born with limbs to begin with. These so called congenital phantom limbs are very strange because their owners obviously have no memories of limbs. Re-membering cannot explain this.

Perhaps it is time to turn from psychology to neuroscience in our quest to understand this trick. The part of the human brain responsible for limb movements is a well organised bit of cortex which looks very similar across people: the primary motor cortex. When the appropriate bit of my own primary motor cortex once got stimulated with magnetic waves, my index finger twitched. Peter Brugger and colleagues did the same with a woman only known as A.Z.. She was born without arms or legs but reported feeling them nonetheless. Magnetic stimulation of her primary motor cortex made her phantom limbs move. This suggests that the action control mechanism and the brain mechanism responsible for phantom limbs are linked.

Thus, all we know about action control in the human brain can be used to explain away the phantom limb phenomenon. Firstly, the primary motor cortex is at least partly genetically determined, i.e. limb control is part of our genetic make-up whether we’ve got limbs or not. When trying to control limbs which do not exist, the brain may create the illusion of controlling phantom limbs instead. Secondly, some researchers believe that a muscle activation command is not only sent to the muscles but a copy is also sent to the back of the brain. This allows us to react to expected action outcomes even before they have occurred. Phantom limbs may occur because expected actions get misinterpreted as real ones. Thirdly, mirror neurons code for actions seen and actions done. According to this explanation A.Z. saw many people use their limbs and this made her have the illusion that she could do the same, albeit only with phantom limbs instead of real ones.

A Greek statue depicting phantom limbs.

However, the final prestige defies all these explanations. Something else entirely must be responsible for a phenomenon reported by Vilayanur Ramachandran and Paul McGeoch in 2008: phantom penises. Like phantom limbs they can occur after amputation. Fascinatingly though, they were also reported by female-to-male transsexuals without an artifical penis. Crucially, this cannot simply be put away as ‘wishful thinking’. For one, their phantom penises were not perfect: for some they were shaped in an undesirable way, erected in embarrassing non-erotic situations, or rubbing against the jeans. But more importantly, Western society goes to great lengths to make life as a transsexual seem like an unattractive option. For example, when they were children, two phantom penis owners were taken to a psychiatrist by their puzzled parents to be treated for a penis that did not exist. Why would anyone want to go through this as a child – or indeed through life changing surgery as an adult – if it wasn’t absolutely necessary?

But if being born with a phantom penis cannot be explained by re-membering, brain mechanisms of action control (a penis is obviously not a muscle one can voluntarily control), or wishful thinking – then what lies behind this phenomenon? This final trick of the mind, seemingly the most ordinary sensation of being a man or a woman in a male or female body, defies easy solutions. Ramachandran and McGeoch speculate that hormonal factors before birth could be responsible.

Before any such speculation can be substantiated I can only conclude that this final prestige remains a mystery. Just like an audience member seeing a magician do a trick on a member of the public, I wonder whether I have been tricked as well. Phantom limbs and phantom penises show powerfully that the link between our anatomical body and our body image is a fragile one. The mind is doing all sorts of trickery behind the scenes in order to hide this difference between body felt and body seen. Like with any good magician, one wonders how this trick is actually done.

‘What’s this? A potato?’ asked my friend’s grandfather during lunch. As always, he used his charming grin and characteristically loud voice. Even though the entire conversation was in Argentine Spanish – which I had learned only a short while before – I understood the oddity of the situation at once. Instead of a potato, the grandfather held a kiwifruit in his hands.

After only a short time of living with this family I noticed that the grandfather no longer had the mental abilities he once must have possessed in order to lead a successful business and raise an adorable family. He was undiagnosed but his behaviour reminded me of Mild Cognitive Impairment, which can progress to a more severe general cognitive impairment – Alzheimer’s Disease or more generally dementia – which usually cannot be cured. ‘What can be done?’ I was asked by my friend’s grandmother afraid of slowly losing the husband she had shared most of her life with. In broken Spanish I tried to explain to her what I would do: build up a cognitive reserve. This concept – related to the beneficial effects of, for example, high education or mentally demanding spare time activities – is perhaps the most promising strategy for delaying dementia.

A large scale analysis illustrates what a cognitive reserve can achieve. First of all, it can delay dementia. An Australian research team (Valenzuela & Sachdev, 2006) collected studies which recruited old people when they were still perfectly healthy and then tested them again after a few years to find out by how much their cognitive abilities had declined. The trend across more than 47,000 people was for higher education and more demanding leisure activities to slow down the creeping loss of mental abilities leading to dementia.

A German nun without experimental confounds.

The savvy reader may already notice a problem with this theory: high education is associated with a generally healthier lifestyle. Rather than cognitive reserve, we should perhaps simply be talking about healthy vs. non-healthy life styles. A Bavarian study ruled this problem out (Bickel & Kurz, 2009). They gained access to the education and dementia records of older female members of a religious order who lived as similarly as one can imagine. The 442 participants had shared a roof for more than five decades, shared meals together, had the same access to medical care. None smoked. None had any personal items. And still, 39% of sisters with low education suffered from dementia, compared to only 14% in the remaining group. Clearly, whether life style has an effect or not, the benefits of a cognitive reserve cannot be reduced to it. It delays dementia all by itself.

This beneficial effect of a cognitive reserve led me to give my advice. However, this strategy cannot stave off dementia forever or even slow it down once it kicks in. Nikolaos Scarmeas and colleagues from Columbia University (2006) found that more highly educated New Yorkers above 65 lose their memory faster around the time of an Alzheimer’s disease diagnosis compared to less educated city dwellers. Apparently, the benefits of a high education are absent around the time of diagnosis.

This raises the obvious question whether my advice was perhaps too late. Once on the road to Alzheimer’s there may be no turning back and efforts to delay the inevitable could make things worse. Given what we know about how the cognitive reserve actually works, I do not believe that this is true. First of all, a cognitive reserve is no cure against dementia but merely a way to delay it. The theory goes that brain pathology progresses whether you have a cognitive reserve or not. What a high education level and demanding leisure activities actually do is to avoid the usual outcome of brain pathology – e.g., easily noticeable memory problems of the kind I have described above. This is supported by studies which compared the brains of people with equal mental function in high age. Those with higher education have more amyloid deposits – a peptide associated with Alzheimer’s disease – as if they were able to deal with their reduced brain function in a better way (Kemppainen et al., 2008; Rentz et al., 2010). At some point though, the progressively worse brain function catches up with you and the resulting cognitive decline is faster.

Charles Hall and colleagues (2007; 2009) tested this overall model in the real world. His analyses of memory test scores of over 100 Bronx residents over the years shows the predicted trend. At first, a high cognitive reserve – whether education or leisure activities – delays the point in time when mental abilities suddenly decline rapidly. Each year in education delays this moment by two and a half months. Each day of mentally stimulating leisure activities delays it by two months. Once this moment is reached, though, the decline is faster with a higher cognitive reserve – as if the aforementioned brain pathology catches up. A cognitive reserve helps you to delay dementia but not to escape it.

The higher the education the shallower the decline before a break point, the later that break point, and the steeper the decline thereafter.

My friend’s grandfather had long been out of education. But the second source of a cognitive reserve – mentally demanding leisure activities – was not beyond him. What sort of activities work? A French research team led by Tasnime Akbaraly (2009) took a better look. They found that only a certain kind of leisure activity will delay dementia onset. Watching television and other passive behaviours won’t do. Neither do physical activities like going for a walk. Nor social ones like have friends or family over. The crucial set of activities are the mentally demanding ones: doing crosswords, playing cards, attending organisations, going to the cinema/theatre, practicing an artistic activity etc.

It is a mystery to me why this knowledge is not more widely spread. Dementia is one of the central challenges facing an ageing population as well as many old couples individually. Research shows that one does not need to be a passive spectator of mental decline. If a cognitive reserve has been built up, one can enjoy more years without showing signs of an incurable disease. That’s what I tried to say in broken Spanish to my friend’s grandmother: make him use his mind.